Last I checked (admittedly a couple of years ago), they also did some tracking behind the scenes, in the bit of code that they had pointedly not released. The undercurrent vibe at the time was that there was no real guarantee that they wouldn't shop around your aggregated data; all I read in that interview is that they have not been "forced" to do it yet, but hey, "life is life" kinda thing. They still do little more than throwing tarballs over the fence every once in a while, with a muddy license that follows the letter rather than the spirit of opensource. There is no real bugtracker nor transparent development practices.

I understand why they do it (people gotta eat), but to me that looks even less trustworthy than Mozilla, which at least has a certain entrenched culture that typically tries (not always successfully) to blunt the worst corporate decisions, and follows real opensource practices.

My impression is that they've explicitly advertised their intention not to sell user data:

  We’ve always taken data security extremely seriously. And we’ve long believed that everything you store in your browser belongs to you — which is why we’ll never sell your data, or willingly compromise your privacy

New copy on the day Chrome is in the middle of a privacy-related storm, what a coincidence.

From the (older) interview you linked: 'The aim is to earn a dollar per year per user. "We're almost there," he says. "I think we can do more than that and still be nice guys and not sell out our users or do anything silly."' That's hardly cast-iron, especially considering that Opera did indeed sell out eventually (yeah I know that "it was complicated", but that's basically what it boiled down to). But hey, in the end, trust is individual, so more power to them. I just think their impact on the web at large will never be as significant as Mozilla's, if they continue on this track.

Opera had investors who pressured Jon, Jon left, they sold out. Vivaldi is Jon & Tatsuki project, no external investors.